Mars’ atmosphere is thin and cold, composed primarily of carbon dioxide along with other trace gases and some water vapor. Evidence has continued to mount, however, that the rarified atmosphere we see today once used to be much thicker and possibly warmer, making it potentially more life-friendly early on. Just how thick and how warm is still a subject of much debate, but there is also another interesting aspect to all of this: New evidence from the Curiosity rover has shown that the Martian atmosphere also used to have a lot more oxygen in it than it does now. Today, only very small traces of oxygen can be found, as opposed to Earth’s oxygen-rich atmosphere. So what does this mean? Could there be biological implications?
It had already been assumed that there must have once been more oxygen (O2) than there is now, to account for all of the reddish iron oxide (rust) on the surface, which would require both water and oxygen. Other studies have also supported this hypothesis, and suggested that there used to be more oxygen, but now the new data from Curiosity indicates that there was probably even more oxygen than first thought. That clue comes from the high levels of manganese oxide found in some rocks by the rover. It is the most direct evidence found so far for a previous oxygen-rich atmosphere earlier in Mars’ history.
“We found 3 percent of rocks have high manganese oxide content,” said Agnès Cousin of the Research Institute in Astrophysics and Planetology in Toulouse, France, at the European Geophysical Union meeting in Vienna, Austria, last week, and reported in New Scientist. “That requires abundant water and strongly oxidising conditions, so the atmosphere may have contained much more oxygen than we thought.”
Almost all of that oxygen escaped to space as the atmosphere thinned over the next few billion years. Now there are only tiny trace amounts left.
It’s also interesting to note that many of the manganese oxide deposits are close to where there used to once exist a lake inside Gale crater, where the rover has been exploring since 2012. That flowing water with dissolved oxygen in it may have helped to create the deposits. It is not yet known exactly how old the deposits are, but additional data from Curiosity should help to determine that.
Of course, the presence of oxygen brings up other questions, relating to possible biological implications. On Earth, by far most of the oxygen is produced by living organisms, via photosynthesis, but what about Mars? Could this be evidence for life early in Mars’ history? Perhaps, although there are other possibilities. Oxygen can also be produced by ultraviolet radiation from the Sun breaking down carbon dioxide, the electrolysis of water, or the photolysis of ozone. Typically, those sources produce much smaller amounts of oxygen. Earth’s atmosphere is rich in oxygen because organisms keep replenishing it, and the gas remains stable. Whether Mars’ atmosphere once being rich in oxygen also points to a biological origin is simply unknown at this point, but it’s possible. Also, while oxygen is produced by some organisms, it can be deadly for others.
As interestingly noted by Damien Loizeau of the University of Lyon in France, “O2 is bad for life as we know it, but we only know life to be able to create large amounts of O2.”
In other Curiosity news, the rover has just completed its latest drilling of a Martian rock, at a location called Lubango, on the Naukluft Plateau, where the rover has been driving for the past several weeks. Mastcam multispectral characterization of the drill hole, followed by several Mastcam mosaics, helps scientists to differentiate between altered and unaltered sandstone bedrock here. Earlier results from ChemCam showed that the Lubango bedrock contains a lot of silica. Curiosity had previously already passed Cubango, but the evidence for high amounts of silica prompted the rover team to return to this location for drilling purposes.
Previous drilling campaigns by Curiosity have added to the growing evidence that Gale crater was once a much more habitable region; the crater itself was once a lake or series of lakes and streams used to cut through the crater walls and empty into that lake(s). It is incredible to think that the area where Curiosity has been roving was at one time a lake bottom, and indeed the rover has also found and examined sediments, mudstone outcrops, and riverbed gravel deposits just like those found on Earth. The finding that there used to be much more oxygen in the atmosphere at the time makes this region of ancient Mars seem even more Earth-like. Curiosity has also found organic compounds in the mudstones, some of which hint at more complex ones, but whether any of them are related to past life is not yet known. From the paper:
“As of today, it is undetermined if the origin of those molecules is biotic or abiotic. However, the variety of molecules detected is consistent with the ones found in meteorites such as Murchison or Tissint.”
Curiosity has now almost finished crossing Naukluft Plateau, which featured some of the most rugged terrain yet seen during the mission. The wheels have taking a beating during the mission so far, but the mission team said that there hasn’t been too much new damage recently. A full 360˚ panorama of the plateau can be seen here.
“We carefully inspect and trend the condition of the wheels,” said Steve Lee, Curiosity’s deputy project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Cracks and punctures have been gradually accumulating at the pace we anticipated, based on testing we performed at JPL. Given our longevity projections, I am confident these wheels will get us to the destinations on Mount Sharp that have been in our plans since before landing.”
Curiosity also recently examined large Martian sand dunes up close for the first time ever (as opposed to smaller sand drifts which other rovers and landers have also seen). These massive, dark dunes extend part way around the base of Mount Sharp, which sits in the middle of Gale crater. High Dune and Namib Dune, part of the Bagnold Dunes field, towered over the rover. These dunes are active, in that they are still slowly progressing over the landscape, like dunes in desert regions of Earth. They show how Mars is still in many ways an active world, with winds strong enough to create these magnificent natural works of art. After finishing on Naukluft Plateau, Curiosity will continue its journey closer to the slopes of Mount Sharp and into the valleys and mesas in the foothills. The scenery here is indeed picturesque, reminiscent of the deserts in the American southwest.
“The only thing more stunning than these images is the thought that Curiosity will be driving through those lower hills one day,” said Curiosity Project Scientist Ashwin Vasavada. “We couldn’t help but send a postcard back to all those following her journey.”
The next region, before getting into the foothills, is more of the lakebed terrain that the rover had traveled on before. Curiosity has now traveled a total of 7.9 miles (12.7 kilometers) since landing in August 2012.
More information about the Curiosity mission is available here.